The present invention relates to an inflator suitable for inflating an airbag or the like for protecting an occupant in a vehicle.
In U.S. Pat. No. 6,273,462, an inflator for inflating an airbag for protecting an occupant in a vehicle has been disclosed. When actuated, an initiator generates a shock wave to open a gas exit. FIG. 2 is a cross sectional view of the inflator disclosed in U.S. Pat. No. 6,273,462.
An inflator 100 is provided with a substantially cylindrical pressure container 104 having a gas storage 102 filled with a high-pressure gas. A gas jet port 106 formed as a circular opening is provided at an axial end (distal end) of the pressure container 104. A burst disk 108 formed of a metal sheet or the like closes the gas jet port 106. The burst disk 108 is adapted to be burst and open the gas jet port 106 when a pressure in the gas storage 102 exceeds a predetermined value, or when an initiator 116 applies a shock wave, which will be described later.
An initiator housing 114 for storing the initiator is provided at the other end (rear end) of the pressure container 104. The initiator housing 114 has a substantially cylindrical shape projecting from the rear end of the pressure container 104 into the gas storage 102 toward the gas jet port 106. The initiator 116 for generating a shock wave is installed in the initiator housing 114.
The initiator 116 is actuated when a pair of electrodes 118, 120 extending from a rear end thereof for conducting power is energized. The initiator generates a gas with a pressure higher than an internal pressure of the gas storage 102. A difference in the pressures is sufficient for generating a shock wave in the gas storage 102. The initiator ejects the high-pressure gas instantaneously from the distal end thereof into the gas storage 102.
In the inflator 100 thus constructed, when the initiator 116 is actuated and the high-pressure gas is ejected from the initiator 116 into the gas storage 102, a shock wave is generated in the gas storage 102 due to the pressure difference between the pressure of the gas from the initiator 116 and the pressure of the gas in the gas storage 102. The shock wave is propagated in the gas storage 102 toward the gas jet port 106. When the shock wave reaches the burst disk 108 closing the gas jet port 106, the burst disk 108 is burst due to the shock wave before a total pressure in the gas storage 102 reaches to a bursting pressure of the burst disk 108, and thus the gas jet port 106 is opened. As a result, the gas is ejected from the inflator 100.
In the inflator 100, a substantially cap shaped diffuser 110 is fitted on the gas jet port 106 at the distal end of the pressure container 104. Therefore, when the burst disk 108 bursts, the gas in the gas storage 102 passes from the gas jet port 106 through the diffuser 110, and is ejected to the outside through orifices 112 formed on a peripheral side surface of the diffuser 110.
As described above, in the inflator 100, the gas is ejected through the jet port 106 when the burst disk 108 is broken before the total gas pressure in the gas storage 102 reaches the burst strength of the burst disk 108. Thus, the gas with a relatively low pressure may be ejected from the jet port 106 for a relatively long period of time. Consequently, the airbag may be inflated relatively slowly and the internal pressure of the airbag may be maintained at a high level for a relatively long period of time.
In the inflator 100 shown in the FIG. 2, the initiator 116 is adapted to generate the shock wave by ejecting the gas toward the inside of the high-pressure gas storage 102, and thus the initiator 116 is required to have a high-performance to rapidly generate the gas with a pressure sufficiently higher than that of the gas filled in the gas storage 102. When an initiator having an inferior performance is used, it is possible that the generated shock wave is not strong enough, and thus may not reach the burst disk 108, or even if it reaches, it may be too weak to burst the burst disk. Therefore, in such a case, it is necessary to shorten a length of the pressure container of the inflator so that the shock wave can reach the burst disk.
It is an object of the present invention to provide an inflator in which a shock wave is generated even when the initiator does not rapidly generate the high-pressure gas as described above, and the shock wave breaks the gas exit of the pressure container to allow the gas to be ejected.
Other objects and advantages of the invention will be apparent from the following disclosure of the invention.
An inflator according to the present invention includes a pressure container having a gas exit that opens upon receipt of a shock wave at one end and being filled with a high-pressure gas therein, and a shock wave generator provided on the other end of the pressure container for generating the shock wave toward the gas exit. The shock wave generator has a tube and an initiator. The tube has a distal end that is broken when the distal end receives the shock wave from inside. The shock wave passes through the distal end toward the gas exit of the pressure container. The tube is filled with a gas having a pressure lower than that of the high-pressure gas in the pressure container. The initiator is provided at a rear end of the tube for emitting the shock wave into the tube when the inflator is actuated.
In the inflator according to the present invention as described above, when the initiator is actuated, the shock wave is generated in the tube by a pressure difference between the gas generated by the initiator and the gas in the tube. Then, the distal end of the tube that received the shock wave is broken to generate additional shock wave due to the pressure difference between the gas in the tube and the gas in the pressure container. The shock wave propagates rapidly in the pressure container, reaches the gas exit of the pressure container, and breaks the gas exit to open. Accordingly, the gas is ejected from the pressure container.
In the present invention, the initiator is provided in the tube filled with the gas having a relatively low pressure. The initiator ejects the gas toward the inside of the tube to generate the shock wave. Therefore, the shock wave can be generated even when the gas pressure generated upon the actuation of the initiator is lower than that of the initiator 116 in the above-described U.S. Pat. No. 6,273,462. Therefore, it is possible to use the initiator with a simple structure and a low cost.
The inflator of the present invention is preferably provided with a booster for promoting the generation of the shock wave by the initiator in the tube.
The booster includes, for example, a propellant (gas forming agent) that induces a gas generation reaction when the initiator generates the gas. When the initiator generates the gas, the booster generates the gas as well to increase the gas pressure generated by the initiator, thereby promoting the generation of the shock wave in the tube.
With the booster provided in the tube, the initiator can have a lower output to generate the shock wave. Therefore, it is possible to use the initiator with a further simpler structure and a lower cost. Even when a pressure container of relatively high capacity is used, or an internal gas pressure is set at a high value, it is possible to use the initiator that can only generates a relatively low-pressure gas to generate the shock wave strong enough for opening the gas exit of the pressure container.